Many major advances in pharmacology have been due to the isolation and identification of proteins or polypeptides endogenous to biological systems.
For example polypeptides isolated from thymus tissue are significant pharmacologically because of their roles in developing, maintaining, restoring or stimulating the immune response and competence in animals, including man.
In particular a fraction has been prepared from calf thymus extracts and designated Thymosin Fraction 5. Studies have shown that Thymosin Fraction 5 is a potent immunopotentiating preparation and that it can act in lieu of the thymus gland to reconstitute immune functions in thymic deprived immunodeficient individuals. Peptides which have been isolated from Thymosin Fraction 5 include thymosin .alpha..sub.1, an acidic peptide containing 28 amino acid residues, the structure of which has been described in U.S. Pat. No. 4,079,127, and thymosin .beta..sub.4 containing 44 amino acid residues, the structure of which has been described in Low, T.L.K., et al., Proc. Nat. Acad. Sci. 78, 1162-1166 (1981).
Another peptide, designated thymosin .beta..sub.8 and having the formula ##STR1## has also been isolated from Thymosin Fraction 5. The structure and isolation of thymosin .beta..sub.8 has been disclosed in U.S. patent application Ser. No. 334,420, filed on Dec. 24, 1981, with common inventorship, and entitled Immunopotentiating Peptides from Thymus.
Thymosin Fraction 5 has been isolated from calf thymus by the procedure of Goldstein et al., Proc. Nat. Acad. Sci. 69, 1800-1803 (1972) and thymosin .alpha..sub.1, thymosin .beta..sub.4 and thymosin .beta..sub.8 were prepared from the isolated Thymosin Fraction 5 by methods well known in the art and purified to be essentially free of other proteinacious substances as by conventional chromatographic methods such as by a combination of ion-exchange chromatography and gel filtration as by the methods described by Goldstein et al., Proc. Nat. Acad. Sci. USA 74, 725-729 (1977), Low et al., J. Biol. Chem. 254, 981-986 (1979) and Low et al., Proc. Nat. Acad. Sci. USA 78, 1162-1166 (1981).